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Chapter 7

Psyc 211 Chapter 7

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PSYC 211
Yogita Chudasama

25.1.13 Chapter 7 Audition, the Body Senses, and the Chemical Senses Behavioural Neuroscience Definitions: Audition Stimulus- • Pitch:Aperceptual dimension of sound; corresponds to the fundamental frequency • Hertz: Cycles per second • Loudness:Aperceptual dimension of sound; corresponds to intensity • Timbre:Aperceptual dimension of sound; corresponds to complexity Anatomy- • Tympanic membrane: The eardrum • Ossicle: One of the three bones of the middle ear • Malleus: The”hammer”; the first of the three ossicles • Incus: The “anvil”; the second of the three ossicles • Stapes: The “stirrup”; the last of the three ossicles • Cochlea: The snail-shaped structure of the inner ear that contains the auditory transducing mechanisms • Oval Window: an opening in the bone surrounding the cochlea that reveals a membrane, against which the baseplate of the stapes presses, transmitting sound vibrations into the fluid within the cochlea • Organ of Corti: The sensory organ on the basilar membrane that contains the auditory hair cells • Hair cells: The receptive cell of the auditory apparatus • Deiters's cell:Asupporting cell found in the organ of Corti; sustains the auditory hair cells • Basilar Membrane:Amembrane in the cochlea of the inner ear; contains the organ of Corti • Tectorial membrane:Amembrane located above the basilar membrane; serves as a shelf against which the cilia of the auditory hair ells move • Round Window:An opening in the bone surrounding the cochlea of the inner ear that permits vibrations to be transmitted, via the oval window, into the fluid in the cochlea Auditory Hair cells & Transduction- • Cilium:Ahair like appendage of a cell involved in movement or in transducing sensory information; found on the receptors in the auditory and vestibular system • Tip link:An elastic filament that attaches the tip of one cilium to the side of the adjacent cilium • insertional plaque: The point of attachment of a tip link to a cilium Auditory Pathways- • Cochlear nerve: The branch of the auditory nerve that transmits auditory information from the cochlea to the brain • Olivocochlear bundles:Abundle of efferent axons that travel from the olivary complex of the medulla to the auditory hair cells on the cochlea • Cochlear nucleus: One of a group of nuclei in the medulla that receive auditory information from the cochlea • Superior olivary complex:A group of nuclei in the medulla; involved with auditory functions, including localization of the source of sounds • Lateral lemniscus:Aband of fibres running rostrally through the medulla and pons; carries fibres of the auditory system • Tonotopic representation:Atopographically organized mapping of different frequencies of sound that are represented in a particular region of the brain • Core region: The primary auditory cortex, located on a gyrus on the dorsal surface of the temporal lobe. Perception of Pitch- • Belt region: The first level of auditory association cortex; surrounds the primary auditory cortex • Parabelt region: The second level of auditory association cortex; surrounds the belt region • Place code: The system by which information about different frequencies is coded by different locations on the basilar membrane • Cochlear implants:An electrical device surgically implanted in the inner ear that can enable a deaf person to hear • Rate coding: The system by which information about different frequencies is coded by the rate of firing of neurons in the auditory system Perception of Timbre- • Fundamental frequency: The lowest, and usually most intense, frequency of a complex sound; most often perceived as the sound's basic pitch • Overtone: The frequency of complex tones that occurs at multiples of the fundamental frequency Perception of complex sounds- • Amusia: Loss or impairment of musica abilities, produced by hereditary factors or brain damage Somatosenses Stimuli- • Cutaneaous sense: Sensitivity to stimuli that involve the skin • Proprioception: Perception of the body's position and posture • Kinesthesia: Perception of the body's own movements • Organic sense:Asense modality that arises from receptors located within the inner organ of the body Anatomy of Skin- • Glabrous skin: Skin that does not contain hair; found on the palms and the soles of the feet • Ruffini Corpuscle:Avibration-sensitive organ located in hairy skin • Pacinian Corpuscle:Aspecialized, encapsulated somatosensory nerve ending that detects mechanical stimuli, especially vibrations • Meissner's Corpuscle: The touch-sensitive end organ located in the Papillae, small elevations of the dermis that project up into the epidermis • Merkel's Disk: The touch-sensitive end organ found at the base of the epidermis, adjacent to sweat ducts Perception of pain: • Phantom limb: Sensation that appear to originate in a limb that has been amputated • Nucleus Raphe Magnus:Anucleus of the raphe that contains serotonin-secreting neurons that project to the dorsal grey matter of spinal cord and is involved in analgesia produced by opiates Notes from each Section: Audition The Stimulus: • We hear sound, produced by objects that vibrate and set molecules in the air into motion, when vibrations range between appr. 30 and 20,000 times per second • The ear is a analytical organ, “to undo,” Two different frequencies of sound waves are mixed, we do not precieve an intermediate tone; instead, we hear both tones. Ex)Able to hear sounds of different instruments in music Anatomy of the Ear: • Sound is funnelled via the pinna( external ear) through the ear canal to the tympanic membrane (eardrum), which vibrates with the sound. • The middle ear consists of a hollow region behind the tympanis membrane, appr. 2 mm in volume • Middle ear consists of: Ossicles, Malleus, Incus, Stapes, Cochlea, and Oval Window. (See definitions at top) • The cochlea, in inner ear, is filled with fluid; sounds through the air and transferred into a liquid medium. Process usually inefficient, 99.9% of energy of airborne sounds would be reflected away if the air impinged directly against the oval window of the cochlea. Cochlea looks snail- shaped, 2 and 3 quarter turns in a cylinder, consisting of the Scala Vestibuli( vestibular Stairway), the Scala Media ( Middle Stairway) and the Scala Tympani ( Tympanic stairway) • The receptive organ, known as the organ of Corti, consists of the basilar membrane, the hair cells, and the tectorial membrane. • Sound waves cause the basilar membrane to move relative to the hair cells, bending produces receptor potential • George von Bekesy: The basilar membrane, the portion that bends the most is determined by the frequency of the sound: High-frequency causes the end nearest the oval window to bend • If system was closed, no vibration would be transmitted (liquids are important incompressible) • The baseplate of the stapes vibrates against the membrane behind the oval window and introduces sound waves into the cochlea. Vibrations cause back and forth motion, creating pressure • Middle ear disease causes bone to grow over oval window, suffer major hearing loss yet surgery, fenesration (tiny whole drilled to make round window) can restore hearing Auditory Hair Cells and the Transduction ofAuditory Information: • Two types of auditory receptors, inner and outer • Cochlea contains appr. 3500 inner hair cells and 12,000 outer that form synapses with bipolar cells dendrites • The movement of the basilar membrane and tectorial membrane move cilia as well as the movement of liquid • Cilia are stiff and rigid due to actin filaments surrounded by myosin filaments (proteins) • Adjacent cilia are connected by tip links (top to side) and the site of attachment is the insertional plagues. Under tension. • Fluid near cilia is rich in potassium. Each insertional plaque contains single cation channels (Corey identified it as TRPA1)When cilia bundles are straight, 10 percent appr. open, allowing K+ and Ca2+ to diffuse. When bends toward tallest cilia, opens all channels, depolarizing. Release of neurotransmitters increases. Does opposite when moving the other direction, hyperpolarizes. TheAuditory Pathway: Connections with the Cochlear Nerve • Organ of Corti sends info to brain by Cochlear nerve (bundle of bipolar neurons, cells bodies in Cochlear nerve ganglia) • Nerves have axonal processes (sustaining action potential that protrudes from both ends of soma) Triggers action potential to neurons in the medulla. • Cochlear nerve contains appr. 50,000 afferent axons. Dendrites are appr. 95% of these axons which form synapses with inner hair cells.Axons are think and myelinated. Other 5% ( thin and unmyelinated) form synapses with outer hairs. (1 fibre to 30 outer hairs) • Inner hairs are of primary importance in CNS • Doel and Gluecksohn-Waelsch, Mutation in rats whose cochlea only contain outer hairs cannot hear at all. Thus outer hair cells are effector cells, involved in altering mechanical characteristics of the basilar membrane • Cochlear nerve has afferent and efferent axons. • Source of efferent axons is the superior olivary complex, constituting Olivocochlear Bundle • Neurotransmitters of afferent axons is Glutamate and the efferent secrete acetycholine (inhibitory effect on hair cells) The central auditory system • Figure above outlines the major pathways • Different parts of the basilar membrane respond best to different frequencies of sound, this relationship between the cortex and basilar membrane is referred to as tonotopic representation • The primary auditory cortex lies hidden on the upper bank of the lateral fissure • Core region, consists of three regions which receives a separate tonotopic map of auditory info from the ventral division from the medial geniculate nucleus. • First level ofAuditory association cortex, the belt region which receives information from the primary auditory cortex and the dorsal and medial geniculate division of the medial nucleus. • Highest level, parabelt region which receives information from the belt region and from the divisions of the medial geniculate nucleus. • Two streams, dorsal ( involved with sound localization) and ventral ( analyses of complex sound) Perception of Pitch: Place Coding • Von Bekesy, acoustic stimuli of different frequencies cause different parts of the basilar membrane to flex (High-frequency means flexing at end near stapes) Meaning some sounds waves are detected by place code • Code represents a means by which neurons can represent information. • Stebbins, found that the progressive death of hair cells is induced by an antibiotic closely parallels a progressive hearing loss: High-frequency go first then low-frequency • Evidence of place coding is cochlear implants. Important for speech as it is formed of high- frequency. Outer m
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